selftests: ncdevmem: don't retry EFAULT

devmem test fails on NIPA. Most likely we get skb(s) with readable
frags (why?) but the failure manifests as an OOM. The OOM happens
because ncdevmem spams the following message:

recvmsg ret=-1
recvmsg: Bad address

As of today, ncdevmem can't deal with various reasons of EFAULT:
- falling back to regular recvmsg for non-devmem skbs
- increasing ctrl_data size (can't happen with ncdevmem's large buffer)

Exit (cleanly) with error when recvmsg returns EFAULT. This should at
least cause the test to cleanup its state.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250904182710.1586473-1-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>